βινκριστίνη θειική

Vinca alkaloid, used in the treatment of several types of cancer. It is administered intravenously weekly.

Vincristine was not detected in any of the milk samples from a treated mother. ^{(Codacci 2019)}

In spite of a pharmacokinetic data (large molecular weight, high plasma protein binding and large volume of distribution) that would make it unlikely the passage to milk of significant amounts along with a low bioavailability that would hinder the passage to infant plasma, most experts advise against the use of anti-neoplastic drugs during lactation due to a potential harmful effect on the infant ^{(Anderson 2016, Koren 2013, Pistilli 2013, Pentheroudakis 2010)} until safety data with relation to breastfeeding are provided.

It is known from pharmacokinetics that after 3 elimination half-lives (T½), 87.5% of the drug is eliminated from the organism; after 4 T½ it is 94%, after 5 T½, 96.9%, after 6 T½, 98.4% and after 7 T½, 99%. From 7 T½ the plasma concentrations of the drug in the body are negligible. In general, a period of at least five half-lives can be considered a safe waiting period before breastfeeding again. ^{(Anderson 2016)}

Taking the longest published T½ of all the active metabolites (155 hours) as a reference, these 5 T½ would correspond to 32 days.

Due to major side effects, it would be advisable to wait 7 T½, which would correspond to 45 days. Meanwhile, express and discard milk from the breast regularly to maintain production.

The pattern of administration and the long elimination half-life make it very difficult to continue breastfeeding during treatment.

When it is possible to do so, milk detections of each patient to determine the total elimination of the drug would be the best indicator to resume breastfeeding between two cycles of chemotherapy.

Chemotherapy does not affect milk production during or after treatment.

Abrupt weaning can be psychologically traumatic for both the mother and the infant. ^{(Pistilli 2013).}

If the mother wishes, production of milk can be maintained by regularly expressing breastmilk, being able to resume breastfeeding in the periods in which no significant traces of the drug remain in the milk (Anderson 2016) or at the end of the treatment. ^{(Pistilli 2013).}

A mother with non-Hodgkin's lymphoma treated with 4 cycles of 21 days of rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone expressed and discarded milk the first 10 days of each cycle (3 T½ vincristine) and breastfed the next 10 days before of the next treatment, without problems for the infant. ^{(Hersey 2020)}

Some chemotherapeutic agents with an antibiotic effect can alter the composition of the microbiota (bacterial set or bacterial flora) of the milk and the concentration of some of its components ^{(Urbaniak 2014)}. This possibly occurs temporarily with subsequent recovery, although no harmful effects are assumed or have been reported in breastfed infants.

Women undergoing chemotherapy during pregnancy have lower rates of breastfeeding because they experience difficulties in breastfeeding ^{(Stopenski 2017)}, needing more support to achieve it.

Given the strong evidence that exists regarding the benefits of breastfeeding for the development of babies and the health of mothers, it is advisable to evaluate the risk-benefit of any maternal treatment, including chemotherapy, individually advising each mother who wishes to continue with breastfeeding. ^{(Koren 2013).}